This proposal is aimed at exploring the detailed molecular interactions between factors encoded in the nuclear genome with factors encoded by the mitochondrial genome. Dr. Moraes, who has extensive experience in characterizing mtDNA mutations in patients with various human mitochondropathies, here aims to study the interaction between factors encoded by the nuclear and mitochondrial genomes by creating and characterizing a heterologous system of primate cell lines harboring nuclear DNA from one species and mitochondrial DNA from another, so-called "xenomitochondrial cybrids." Thus, biological functions that involve coordinated participation of nuclear-coded and mtDNA-coded factors may be affected in these cell lines. The P.I. suggests that biochemical and molecular studies of these cell lines will shed light on many nDNA-mtDNA interactions that are needed for mtDNA transcription and replication, assembly of respiratory complexes and ATP production, mitochondrial protein synthesis, mitochondrial posttranscriptional modifications of RNA, mtDNA heteroplasmy dynamics, and mtDNA recombinations, all of which are essential for the establishment and maintenance of an efficient ATP generating system.